1. Field of the Invention
This invention relates to the field of sub band filtering. More particularly, this invention relates to the flow of data through sub band filters.
2. Description of the Prior Art
Sub band filtering is a process by which a signal is divided into a number of consecutive bands in the frequency domain. In one known application, these bands are processed independently to produce a compressed representation of the original signal, and later reconstructed, using further filters, to reproduce the original signal. For example, sub band filtering may be used to carry out decorrelation of image data in the two dimensional spatial frequency domain within an image data compression system.
Known multi-stage sub band filters, based on separate filter banks, are arranged in a tree structure as shown in FIG. 1. Each stage in the filter further divides the data into more sub bands. In the example shown, which is based upon high and low pass filters, each stage doubles the number of sub bands into which the data is divided.
Such known arrangements involve the disadvantageous use of a large amount of hardware. Also, at each separation stage, the sample throughput rate is reduced by a factor of two on that for the previous stage. Similarly, at each combination stage, sample throughput rate is increased by a factor of two on that for the previous stage. Thus, the known arrangements use a large amount of hardware, most of which is inefficiently operating at below its maximum capacity.